I had those uPA NEC monolithic JFET flatpacks that had very nice curve matching consistency and I wanted to test ideas around them. So I beavered away for one and a half months and there it was. But I tested everything I had, even LND150 mini MOSFETS. The board has LSK389 positions too because not NOS. Closest to uPA THD profile. But uPA are still cheap and available because nobody uses them.

Has a sound smooth as tubes no worries. But combining resolution better than DCB1 even. See how it goes second harmonic as the load gets heavier in the THD attachments. Its the single ended output stage MOSFET nature. 100-150mA bias and virtually zero Ohm output impedance gives bass slam and definition too.

The headphones sound easily more alive bigger and smoother than they did on my Benchmark DAC1. Swiss knife preamp.

Here is IMD SMPTE when driving 120 Ohm for instance. That's strong 250Hz trying to modulate quieter 8kHZ. See the little bass tone modulations around the high tone's base. 0.0027% modulation at 101dB SPL with those AKG. Means clarity in busy music. Not easy to do that with SE tube headphone amp.